1. Field of the Invention
The present invention relates to a post-process sizing control device for measuring a machining portion of a workpiece to control a further infeed amount of a grinding wheel against the machining portion in a grinding machine.
2. Discussion of the Related Art
Generally, for grinding a workpiece, there has been used a numerically controllable grinding apparatus (numerical control grinding machine), wherein the workpiece is rotatably mounted on a work spindle and wherein the feed amount of a wheel head movable in a direction intersecting with the work spindle is controlled in synchronous relation with the rotation of the work spindle to perform a grinding operation. At this time, in order to perform the grinding efficiently, as a method of controlling the size, there has been known a post-process sizing control device which performs a rough grinding until a size with a grinding amount left for finish is reached, then measures the size after the rough grinding of the workpiece by a size measuring device provided in the grinding machine, calculates the difference between the actually measured size and a theoretical size derived from calculation, and compensates the position of the wheel head by a position compensation amount corresponding to the difference.
Then, in actually performing the post-process sizing control as described in JP5-84646 A, consideration has to be given to the following two states: the case of a cold starting, that is, an initial state that electric power is applied to the grinding machine after the same remains in power-off state for a long period of time, and the case of a warmed-up starting, that is, another state that the grinding machine has fully been warmed up by having been operated for a predetermined period of time after the input of electric power. It is well known that the fluctuation in finish sizes is suppressed in the warmed-up state rather than in the initial state of the cold starting. The known device is designed to perform the post-process sizing control at size measuring intervals which depend on program data which has been set in advance. When operated in accordance with the program data, the known device measures the sizes of workpieces at shorter size measuring intervals in the case of the cold starting involving a large fluctuation in sizes, but at longer size measuring intervals so that the measuring is performed at the rate, for example, of one for ten workpieces from the time when it is judged that the grinding machine would have been warmed up, because the fluctuation in sizes becomes small.
However, in the foregoing post-process sizing control device, the post-process sizing control is carried out at the size measuring intervals which have been set in advance, and no considerations are given to machine-dependant differences, the fluctuation in the ambient temperature, the length of the duration in which the grinding machine has been kept in the stop state. It occurs therefore that the post-process sizing control is executed at the size measuring intervals depending on the initially set program even in the absence of the need for size compensations. This causes the machining cycle time to be elongated and hence, the productivity to decline. Accordingly, there has been desired a system which is capable of executing the post-process sizing control at the most suitable size measuring intervals which are flexible in dependence on various states of the grinding machine.